The present invention relates generally to signal probes and more particularly to a multi-channel, low input capacitance signal probe and probe head usable with measurement test instruments, such as logic analyzers and the like.
Logic analyzers have long been used to acquire multiple signals from a device under test to analyze and verify timing, detect glitches, and the like. Multi-channel signal probes couple signals to the device under test from the instrument and from the device under test to the instrument. Various types of connectors are provided on the device under test, such as a microprocessor mother board, for connecting the signal probes to the device being tested. Rows of square pin connectors have traditionally been used as the interface contacts between the device under test and the probes.
The increased speed of digital circuitry requires the use of connectors having high speed, controlled impedance transmission lines. One such connector is called a mictor connector, manufactured by Tyco Electronics, Corp., Harrisburg, Pa. A mictor connector is a high speed, controlled impedance connector having a plug and closely mating receptacle. Each plug and receptacle portion is configured for either 0.025 inch or 0.050 inch center line spacing of transmission lines and contain from 38 to 266 lines. The transmission lines are aligned in parallel rows on either side of center power ground connector. The center ground connector in the plug is a corrugated planar structure that mates with vertically positioned ground leads in the receptacle. The transmission lines in the plug and receptacle are contained in mating housings. Mictor connectors have both vertically and horizontally mounted plugs and receptacles. The ends of the transmission lines extending from the bottom of the vertically mounted plug or receptacle are bent at an angle to form contact pads for soldering to contact pads on the surface of a circuit board or the like. The ends of the transmission lines of the horizontally mounted plug or receptacle extend directly outward from the bottom of the plug or receptacle for soldering to contact pads formed on opposing surfaces of the circuit board or the like at the edge of the board. The ends of the transmission lines at the other end of the housing of the plug or receptacle form electrical contacts that mate with each other when the closely mating plug and receptacle are connected together. In logic analyzer probing applications, a 38 pin mictor connector is most often used. Up to 38 circuit board runs of the device under test are laid out in pattern that terminate in a pattern corresponding to the pattern of the pins on the mictor connectors. The mictor receptacle is soldered to conductive pads that terminate the runs. In most probing applications of microprocessor boards, multiple mictor connectors are mounted on the circuit board. The multi-channel logic analyzer probe head has the mating mictor plug. The transmission lines of the mictor plug are electrically coupled to center conductors of a multiple coaxial cable type ribbon cable. Electrical elements, such as resistors, may be included in the probe head to provide electrical isolation for the device under test.
The P6434 34-channel high density probe, manufactured and sold by Tektronix, Inc., Beaverton, Oreg., for use with the TLA family of logic analyzers is an example of a logic analyzer probe using mictor connectors. The P6434 probe head uses an edge mounted mictor connector that is soldered to contact pads on opposing sides of a circuit board. The circuit board has an additional row of interconnect contact pads formed on each opposing side of the circuit board that are electrically connected via conductive runs to the soldered contact pads of the mictor connector. The mictor connector and circuit board are inserted into a holder that also receives two probe cables. The probe cables are ribbon type cables having multiple lead wires. The lead wires of each probe cable are soldered to contact pads of a circuit board. The contact pads are electrically connected via conductive runs to another set of contact pads that match the interconnect contact pads of the mictor connector circuit board. The conductive runs preferably include resistive elements. The probe cable circuit boards are positioned on the mictor connector circuit board with electrically conductive elastomer contacts electrically connecting the contact pads on the probe cable circuit board to the interconnect contact pads of the mictor connector circuit board. The circuit boards and the mictor connector are secured in place in a housing made of opposing half shells that are screwed together.
There are drawbacks to using mictor connectors and similar type connectors, such as Samtec connectors, for high speed probing applications. The transmission lines of the mictor connector adds capacitive loading to the device under test which affects the fidelity of the signal being acquired. The input capacitance of the mictor connector/probe head combination can be in the range of 2 to 2.5 picofarads. The mictor connectors are permanently mounted on the circuit board, which increases the cost of board, especially when multiple mictor connectors are used. Additionally, the complexity of the device under test board layout is increased because of the need to layout trace runs to each of the mictor connector, which may result in sacrificing board space that may otherwise be used for component layout.
What is needed is a multi-channel, low input capacitance signal probe head for devices under test that reduces the capacitive loading associated with previous types of probe heads using existing high density connectors. In addition, the multi-channel, low input capacitance probe head should eliminate the need for permanently mounted connectors on circuit boards of the device under test. Further, the multi-channel, low input capacitance probe head should provide flexibility in device under test board layout. There is also a need for adapters that connect existing connectors to the new multi-channel, low input capacitance signal probe head and existing multi-channel probe heads to the new connecting elements on the device under test.
Accordingly, the present invention is to a multi-channel, low input capacitance signal probe head usable for acquiring multiple signals from a device under test. The signal probe head has at least a first substrate having a plurality of input signal pads formed and exposed at one end of the substrate. The substrate is positioned in a housing having at least a first open end and a substrate support member that receives the substrate such that the input signal pads are exposed at the open of the housing. A removable signal contact holder mounts to the housing and supports electrically conductive elastomer signal contacts. The holder is disposed over the open end the housing such that the elastomer signal contacts engage the input signal pads. The multi-channel, low input capacitance signal probe head is preferably configured with a second substrate having a plurality of input signal pads formed and exposed at one end of the substrate. The substrate support member receives the second substrate such that the support member is disposed between the first and second substrate and the input signal pads on the second substrate are exposed at the open end of the housing.
The housing preferably has opposing sidewalls walls separated by opposing front and back walls with each sidewall having a latching recess formed therein adjacent to the open end of the housing. The housing has bores formed on either side of the substrate that are perpendicular to the open end of the housing. The housing is preferably configured with a substrate carrier and a substrate carrier cover. The substrate carrier forms the substrate support member that receives the substrate with the input signal pads on the substrate being exposed at one end of the carrier. The substrate carrier cover has exterior walls forming an interior chamber that receives the substrate carrier and substrate with the exterior walls forming the opposing sidewalls and front and back walls of the housing. The substrate carrier has opposing stiles and rails with the stiles and at least one rail having recesses formed on one surface thereof for receiving the substrate with the end of the substrate having the signal pads extending to the end of the rail having the recess. The stiles of the carrier include the housing bores. The carrier may be configured to receive a second substrate having a plurality of input signal pads thereon with the input signal pads being exposed on one end of the substrate. The stiles and the one rail have recesses formed on the reverse side thereof for receiving the second substrate with the end of the substrate having the signal pads extending to the end of the rail having the recess.
The removable signal contact holder preferably has a planar frame member and latching members extending perpendicular from either end of the frame member. At least a first slot is formed in the frame member aligned with the input signal pads on the substrate for receiving the electrically conductive elastomer signal contacts. The latching members have inwardly facing latching ramps with each latching ramp having a terminating ledge that engage the latching recesses in the housing sidewalls. At least a first alignment rib is formed parallel to the slot on the planar frame that engages a corresponding recess formed in the housing. Apertures are formed on either side of the slot that are aligned with the bores in the housing.
A probe head retention member is provided for securing the multi-channel, low input capacitance signal probe head to a device under test. The device under test is preferably a circuit board having an array of signal contact pads on at least one surface thereof corresponding to the electrically conductive elastomer signal contacts. Through holes are formed on either side of the array of signal contact pads. The retention member has a first configuration with attachment members, in the form of threaded screws, extending through the bores in the housing and threadably mating with retention nuts mounted to the opposite side of the circuit board from the contact pads and aligned with the through holes. For this configuration, flanges are formed in the removable signal contact holder adjacent to the apertures and extending in a direction opposite from the latching members. The flanges engage the through holes in the circuit board to align the elastomer signal contacts with the array of signal contacts on the circuit board.
A second configuration for the retention member has attachment members, in the form of threaded screws, extending through the bores in the housing and threadably mating with threaded apertures disposed in a retention block positioned on the opposite side of the circuit board from the contact pads and aligned with the through holes in the circuit board. The retention block has alignment flanges formed adjacent to the threaded apertures that have an exterior surface closely mating with and extending through the through holes in the circuit board. The flanges preferably include latching members extending outward from the flanges to engage the top surface of the circuit board. The alignment flanges extending above the circuit board are closely received in second bores extending into the housing from the open end of the housing and coaxial with the first bores. The second bores have a diameter larger than the first bores with notches formed in the housing adjacent to the open end that closely receive in the latching members.
The retention block is preferably configured with an elongated rectangular housing having exterior walls forming an interior chamber that receives a stiffener block having the threaded apertures formed therein. The rectangular housing has alignment flanges extending from one of the exterior walls adjacent to the threaded apertures with the exterior surfaces of the flanges closely mating with and extending through the through holes in the circuit board. The alignment flanges also include latching members extending outward from the flanges to engage the top surface of the circuit board.
The multi-channel, low input capacitance signal probe head is used in a multi-channel, low input capacitance measurement probe for coupling a device under test having an array of signal contact pads on at least one surface of a circuit board and through holes formed on either side of the array of signal contact pads to a measurement instrument. The measurement probe has a measurement probe head with at least a first substrate having a plurality of input signal circuits and associated input signal pads formed thereon. The input signal pads are exposed on one end of the substrate and the input signal circuits are adjacent to and electrically coupled to the input signal pads. The first substrate is disposed within a housing having a substrate carrier and substrate carrier cover with the substrate carrier receiving the substrate such that the input signal pads on the substrate are exposed at one end of the carrier. The substrate carrier cover has opposing sidewalls separated by opposing front and back walls forming an open ended chamber that receives the substrate carrier and substrate such that the input signal pads are exposed at one of the open ends of the cover. Each sidewall of the cover has a latching recess formed therein adjacent to the open end of the housing. The multi-channel, low input capacitance measurement probe is preferably configured with a second substrate having a plurality of input signal circuits and associated input signal pads formed thereon. The substrate carrier receives the second substrate such that the carrier is disposed between the first and second substrate and the input signal pads on the second substrate are exposed at the end of the carrier.
The probe head is secured to the device under test by a probe head retention member having bores formed through the substrate carrier on either side of the substrate that are perpendicular to the open end of the housing and aligned with the through holes in the circuit board. Attachment members extend through the bores in the substrate carrier and threadably mate with threaded apertures mounted to the opposite side of the circuit board from the contact pads and over the through holes.
A removable signal contact holder mounts over the open end of the housing. The contact holder has a planar frame member and latching members extending perpendicular from either end of the frame member. The frame member has at least a first slot aligned with the input signal pads on the substrate that receives electrically conductive elastomer signal contacts. The latching members have inwardly facing latching ramps with each latching ramp having a terminating ledge that engage the latching recesses in the housing sidewalls to mount the signal contact holder over the open end the housing such that the elastomer signal contacts engage the input signal pads. Apertures are formed on either side of the electrically conductive elastomer signal contacts that are aligned with the bores in the substrate carrier and the through holes on the circuit board. The probe head is coupled to the measurement instrument using a multiple signal lines cable having signal lines at one end electrically coupled to outputs of the input signal circuits and the other ends of the signal lines electrically coupled to an input connector that is coupled to an input connector on the measurement instrument.
A first adapter is provided to connect existing multi-channel signal probes to the signal contact pad configuration used with the multi-channel, low capacitance signal probe of the present invention. Existing multi-channel signal probes are terminated in a connector having mating plug and receptacle portions. The respective plug and receptacle portions have high speed, controlled impedance transmission lines disposed within respective housings. One end of the transmission lines form contact pads at one end of the respective housings and the other end of the transmission lines form electrical contacts at the other end of the housings. The electrical contacts engage each other on mating of the plug and receptacle. The adapter includes the other of the closely mating plug and receptacle. The contact pads of the transmission lines are affixed to a first array of contact pads formed on the top surface of a substrate. The bottom surface of the substrate has a second array of contact pads formed thereon that correspond to the signal contact pads on the circuit board of the device under test. The contact pads on the top surface are electrically coupled to corresponding contact pads on the bottom surface. A removable signal contact holder is positioned adjacent to the bottom surface of the substrate and supports electrically conductive elastomer signal contacts such that the elastomer signal contacts engage the second array of contact pads. An adapter retention member is positioned on the opposite side of the circuit board from the signal contact pads and has attachment members to secure the adapter to the circuit board.
A second adapter is provided to connect the multi-channel, low input capacitance signal probe to a plug or receptacle of a high speed, controlled impedance connector mounted to the device under test. The second adapter has a housing with opposing end walls and sidewalls forming a cavity that receives the other of the closely mating plug or receptacle. The contact pads of the transmission lines of the closely mating plug or receptacle are exposed at one end of the housing cavity and the electrical contacts of the transmission lines are exposed at the other end of the housing. The housing has probe head retention members formed in the sidewalls on either side of the cavity and alignment flanges disposed adjacent to the probe head retention members that extend upward from the sidewalls. The retention members include bores formed in the sidewalls with the bores receiving pins having a threaded aperture formed therein.
The adapter includes a substrate having apertures formed therethrough that closely receive the alignment flanges on the housing. The substrate has first and second arrays of contact pads formed on the respective top and bottom surfaces of the substrate. The first array of contact pads correspond to the electrically conductive elastomer signal contacts of the multi-channel, low input capacitance signal probe head The second array of contact pads are affixed to the corresponding contact pads of the transmission lines of the plug or receptacle. The first array of contact pads on the top surface of the substrate are electrically coupled to the corresponding second array of contact pads on the bottom surface of the substrate via conductive runs extending through the substrate.
The alignment flanges mate with corresponding bores in the multi-channel, low input capacitance signal probe head such that the signal contact pads of the multi-channel, low input capacitance signal probe head connect to corresponding contact pads on the top surface of the substrate. The threaded pins of the probe head retention members receive attachment members, such as threaded screws, disposed in the bores of the multi-channel, low input capacitance signal probe head to secure the probe head to the housing.
The objects, advantages and novel features of the present invention are apparent from the following detailed description when read in conjunction with appended claims and attached drawings.